1. Field of the Invention
The present invention relates to signal adjuster and more particularly, to a signal adjuster for connection between a signal source and a video display device through a high frequency signal cable to enhance the strength of the transmitting high frequency signal by means of an adjustable equalizer subject to the detection of a signal bandwidth detector.
2. Description of the Related Art
In recent years, there is a great change in audio and video application industry. In consequence, a variety of audio and video devices have been developed and intensively used in our daily life. These audio and video devices including CD/VCD/DVD players, high resolution digital TVs, video phones and videoconference systems commonly use a digitalized technology to process audio signal in video signal. Following different application requirements, related protocols have been well defined. For example, DVI (Digital Video Interface) is a connection standard for connection between a display card system and a display device, for particularly, a digital display device. A DVI display card system comprises a transmitter and a receiver. The transmitter can be built in the display card system. DVI is established subject to TMDS (Transition Minimized Differential Signaling) protocol, i.e., PanelLink technology that supports VGA to QXGA (2048×1536) resolution, has the pulse speed of 25˜165 MHz. The bandwidth can reach 1.65 Gbps during transmission under one single channel link, or over 2 Gbps during transmission under two channel links. TMDS allows transmission of digital signal, therefore it is connectable to a conventional CRT monitor.
Early analog TVs adopt analog signal only. Analog signal uses a low frequency as the transmission interface. Low frequency allows transmission of only one signal at a time. The picture quality of an analog TV is less clear. In recent years, digital TVs have been intensively used to substitute for conventional analog TVs. A digital TV accepts transmission of multiple image signals at a time. For transmission of a big amount of video data, a digital TV uses a high-frequency interface for signal transmission. This high-frequency interface is used an application of HDMI (High Definition Multimedia Interface) cable that provides an uncompressed digital link between consumer electronics equipment such as DVD players, set-top boxes and audio/video monitors such as plasma display screens for HDTV's. HDMI supports standard, enhanced, or high-definition video, plus multi-channel digital audio on a signal cable. It transmits all ATSC HDTV standards and supports 4-channel digital audio, with bandwidth to spare to accommodate future enhancements and requirements.
However, when multiple users share one single high frequency signal cable through a router and there is a long distance between transmitter side and receiver side, the signal will be attenuated following the increasing of the distance between the transmitter side and the receiver side, and the images will be interfered with noises. Due to this drawback, a high-frequency interface may be not usable in certain fields. Further, in order to eliminate noises during transmission of a signal to a digital TV through the cable, a signal adjuster may be attached to the transmitter side or the receiver side to enhance the signal.
Although many new video signal transmission interface means have been continuously developing, there is still a limitation to the effective transmission distance. The use of a conventional signal adjuster in a high frequency signal cable still cannot allow a great extension of the length of the high frequency signal cable.